Synthesis of Na-A zeolite from 10 A halloysite and a new crystallization kinetic model for the transformation of Na-A into HS zeolite

The present work deals with the synthesis of Na-A zeolite using 10 angstrom halloysite (collected near Grosseto, Italy) as the starting material, instead of the more expensive chemicals currently used in industry (Na aluminates and Na silicates). The process of synthesizing Na-A zeolite from 10 angstrom halloysite is rather simple as the reaction of halloysite with alkali occurs very readily and is achieved without prior thermal activation at high temperature. The optimal conditions of crystallization of Na-A zeolite from 10 angstrom halloysite are reached at 80 degrees C. At lower temperatures, transformation of halloysite into an amorphous material requires more time, and the field within which Na-A zeolite exists overlaps that of 7 angstrom halloysite, G and HS zeolites. The products of synthesis at 80 degrees C were characterized by X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometry and infrared spectroscopy. We also propose a model to study the reaction kinetics of zeolite (Na-A and HS) nucleation and growth by real-time X-ray powder diffraction data.